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| 1 /* | |
| 2 * Copyright 2004 The WebRTC Project Authors. All rights reserved. | |
| 3 * | |
| 4 * Use of this source code is governed by a BSD-style license | |
| 5 * that can be found in the LICENSE file in the root of the source | |
| 6 * tree. An additional intellectual property rights grant can be found | |
| 7 * in the file PATENTS. All contributing project authors may | |
| 8 * be found in the AUTHORS file in the root of the source tree. | |
| 9 */ | |
| 10 | |
| 11 #ifndef WEBRTC_BASE_TASK_H__ | |
| 12 #define WEBRTC_BASE_TASK_H__ | |
| 13 | |
| 14 #include <stdint.h> | |
| 15 | |
| 16 #include <string> | |
| 17 | |
| 18 #include "webrtc/base/sigslot.h" | |
| 19 #include "webrtc/base/taskparent.h" | |
| 20 | |
| 21 ///////////////////////////////////////////////////////////////////// | |
| 22 // | |
| 23 // TASK | |
| 24 // | |
| 25 ///////////////////////////////////////////////////////////////////// | |
| 26 // | |
| 27 // Task is a state machine infrastructure. States are pushed forward by | |
| 28 // pushing forwards a TaskRunner that holds on to all Tasks. The purpose | |
| 29 // of Task is threefold: | |
| 30 // | |
| 31 // (1) It manages ongoing work on the UI thread. Multitasking without | |
| 32 // threads, keeping it easy, keeping it real. :-) It does this by | |
| 33 // organizing a set of states for each task. When you return from your | |
| 34 // Process*() function, you return an integer for the next state. You do | |
| 35 // not go onto the next state yourself. Every time you enter a state, | |
| 36 // you check to see if you can do anything yet. If not, you return | |
| 37 // STATE_BLOCKED. If you _could_ do anything, do not return | |
| 38 // STATE_BLOCKED - even if you end up in the same state, return | |
| 39 // STATE_mysamestate. When you are done, return STATE_DONE and then the | |
| 40 // task will self-delete sometime afterwards. | |
| 41 // | |
| 42 // (2) It helps you avoid all those reentrancy problems when you chain | |
| 43 // too many triggers on one thread. Basically if you want to tell a task | |
| 44 // to process something for you, you feed your task some information and | |
| 45 // then you Wake() it. Don't tell it to process it right away. If it | |
| 46 // might be working on something as you send it information, you may want | |
| 47 // to have a queue in the task. | |
| 48 // | |
| 49 // (3) Finally it helps manage parent tasks and children. If a parent | |
| 50 // task gets aborted, all the children tasks are too. The nice thing | |
| 51 // about this, for example, is if you have one parent task that | |
| 52 // represents, say, and Xmpp connection, then you can spawn a whole bunch | |
| 53 // of infinite lifetime child tasks and now worry about cleaning them up. | |
| 54 // When the parent task goes to STATE_DONE, the task engine will make | |
| 55 // sure all those children are aborted and get deleted. | |
| 56 // | |
| 57 // Notice that Task has a few built-in states, e.g., | |
| 58 // | |
| 59 // STATE_INIT - the task isn't running yet | |
| 60 // STATE_START - the task is in its first state | |
| 61 // STATE_RESPONSE - the task is in its second state | |
| 62 // STATE_DONE - the task is done | |
| 63 // | |
| 64 // STATE_ERROR - indicates an error - we should audit the error code in | |
| 65 // light of any usage of it to see if it should be improved. When I | |
| 66 // first put down the task stuff I didn't have a good sense of what was | |
| 67 // needed for Abort and Error, and now the subclasses of Task will ground | |
| 68 // the design in a stronger way. | |
| 69 // | |
| 70 // STATE_NEXT - the first undefined state number. (like WM_USER) - you | |
| 71 // can start defining more task states there. | |
| 72 // | |
| 73 // When you define more task states, just override Process(int state) and | |
| 74 // add your own switch statement. If you want to delegate to | |
| 75 // Task::Process, you can effectively delegate to its switch statement. | |
| 76 // No fancy method pointers or such - this is all just pretty low tech, | |
| 77 // easy to debug, and fast. | |
| 78 // | |
| 79 // Also notice that Task has some primitive built-in timeout functionality. | |
| 80 // | |
| 81 // A timeout is defined as "the task stays in STATE_BLOCKED longer than | |
| 82 // timeout_seconds_." | |
| 83 // | |
| 84 // Descendant classes can override this behavior by calling the | |
| 85 // various protected methods to change the timeout behavior. For | |
| 86 // instance, a descendand might call SuspendTimeout() when it knows | |
| 87 // that it isn't waiting for anything that might timeout, but isn't | |
| 88 // yet in the STATE_DONE state. | |
| 89 // | |
| 90 | |
| 91 namespace rtc { | |
| 92 | |
| 93 // Executes a sequence of steps | |
| 94 class Task : public TaskParent { | |
| 95 public: | |
| 96 Task(TaskParent *parent); | |
| 97 ~Task() override; | |
| 98 | |
| 99 int32_t unique_id() { return unique_id_; } | |
| 100 | |
| 101 void Start(); | |
| 102 void Step(); | |
| 103 int GetState() const { return state_; } | |
| 104 bool HasError() const { return (GetState() == STATE_ERROR); } | |
| 105 bool Blocked() const { return blocked_; } | |
| 106 bool IsDone() const { return done_; } | |
| 107 int64_t ElapsedTime(); | |
| 108 | |
| 109 // Called from outside to stop task without any more callbacks | |
| 110 void Abort(bool nowake = false); | |
| 111 | |
| 112 bool TimedOut(); | |
| 113 | |
| 114 int64_t timeout_time() const { return timeout_time_; } | |
| 115 int timeout_seconds() const { return timeout_seconds_; } | |
| 116 void set_timeout_seconds(int timeout_seconds); | |
| 117 | |
| 118 sigslot::signal0<> SignalTimeout; | |
| 119 | |
| 120 // Called inside the task to signal that the task may be unblocked | |
| 121 void Wake(); | |
| 122 | |
| 123 protected: | |
| 124 | |
| 125 enum { | |
| 126 STATE_BLOCKED = -1, | |
| 127 STATE_INIT = 0, | |
| 128 STATE_START = 1, | |
| 129 STATE_DONE = 2, | |
| 130 STATE_ERROR = 3, | |
| 131 STATE_RESPONSE = 4, | |
| 132 STATE_NEXT = 5, // Subclasses which need more states start here and higher | |
| 133 }; | |
| 134 | |
| 135 // Called inside to advise that the task should wake and signal an error | |
| 136 void Error(); | |
| 137 | |
| 138 int64_t CurrentTime(); | |
| 139 | |
| 140 virtual std::string GetStateName(int state) const; | |
| 141 virtual int Process(int state); | |
| 142 virtual void Stop(); | |
| 143 virtual int ProcessStart() = 0; | |
| 144 virtual int ProcessResponse(); | |
| 145 | |
| 146 void ResetTimeout(); | |
| 147 void ClearTimeout(); | |
| 148 | |
| 149 void SuspendTimeout(); | |
| 150 void ResumeTimeout(); | |
| 151 | |
| 152 protected: | |
| 153 virtual int OnTimeout(); | |
| 154 | |
| 155 private: | |
| 156 void Done(); | |
| 157 | |
| 158 int state_; | |
| 159 bool blocked_; | |
| 160 bool done_; | |
| 161 bool aborted_; | |
| 162 bool busy_; | |
| 163 bool error_; | |
| 164 int64_t start_time_; | |
| 165 int64_t timeout_time_; | |
| 166 int timeout_seconds_; | |
| 167 bool timeout_suspended_; | |
| 168 int32_t unique_id_; | |
| 169 | |
| 170 static int32_t unique_id_seed_; | |
| 171 }; | |
| 172 | |
| 173 } // namespace rtc | |
| 174 | |
| 175 #endif // WEBRTC_BASE_TASK_H__ | |
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